Soldiers deployed to a combat zone may have a harder time sleeping, according to a large cohort study.

Action Points

Explain that military personnel deployed to a combat zone may have a tough time sleeping.

Note that the association between combat deployment and insomnia was modified by mental health problems -- including posttraumatic stress disorder (PTSD) and depression -- during follow-up.

Soldiers deployed to a combat zone may have a harder time sleeping, according to a large cohort study.

The study, involving more than 41,000 military personnel, found that sleep duration was significantly shorter for those currently deployed to Iraq or Afghanistan (6.46 hours) or who had completed a deployment (6.47 hours), compared with those who had not been deployed (6.56 hours, P<0.01), Amber Seelig, MPH, of the Naval Health Research Center in San Diego, and colleagues reported in Dec. 1 issue of SLEEP.

Both groups of deployed personnel were more likely to report having trouble sleeping. However, the relationships seemed to be modified by both exposure to combat and by mental health problems -- including posttraumatic stress disorder (PTSD) and depression -- during follow-up.

"If poor sleep contributes to the occurrence, persistence, or severity of mental health disorders or poor job performance, then the promotion of healthier sleep patterns, including recovery time following extreme sleep deprivation, among military service members may be beneficial in this population," Seelig and her colleagues wrote.

The researchers looked at data from the Millennium Cohort Study, a longitudinal study of members of all service branches of the U.S. military, including active-duty, reserve, and National Guard personnel.

The current analysis included 41,225 military personnel who completed both a baseline survey from 2001 to 2003 and a follow-up survey from 2004 to 2006. Of the cohort, 30,190 were not deployed during the study, 9,264 had completed at least one deployment to Iraq or Afghanistan before the final survey, and 1,771 completed the final survey during a deployment to one of those two countries.

The average sleep duration for the month before the survey was self-reported and rounded to the nearest hour. Trouble sleeping was defined as having difficulty falling or staying asleep.

The shorter average sleep duration in the two deployed groups was significant after adjusting for all demographic, military, health, and behavioral variables measured at baseline.

However, the between-group difference disappeared after further adjustment for combat exposure and mental health conditions -- including PTSD, depression, anxiety, and panic -- during follow-up.

Respondents who reported currently being deployed or having completed a deployment were significantly more likely to report having trouble sleeping (odds ratios 1.28 and 1.21, respectively) than those who had not been deployed.

That relationship, too, was modified by the presence of mental health conditions, particularly anxiety (P=0.01).

Among those without panic or anxiety symptoms during follow-up, the greatest odds of having trouble sleeping were for those who reported other mental health disorders, including PTSD (OR 12.91) and depression (OR 12.42).

In this group, soldiers who had completed a deployment actually had lower odds of having trouble sleeping (OR 0.91). Those who had been exposed to combat were more likely to report difficulty sleeping (OR 1.61).

Among respondents who did report anxiety or panic symptoms during follow-up, the greatest odds of having trouble sleeping were also for those with PTSD (OR 3.88) or depression (OR 2.84) -- but at a smaller magnitude than in the respondents free from anxiety or panic during follow-up.

There was no significant difference on the basis of deployment or combat exposure in this subgroup.

"These findings suggest that the relationships between deployment and sleep duration and trouble sleeping are mediated by the effects of combat exposures and mental health symptoms," Seelig and her colleagues wrote, and "merit further research to increase understanding of temporal relationships between sleep and mental health outcomes occurring during and after deployment."

The authors noted some limitations of their study, including the use of self-reported data, which are subject to recall bias, the use of rounded whole number increments for sleep duration, and the inability to adjust for several factors that could affect sleep -- such as the use of prescribed sleep medications, other medications with sleep-related side effects, and stimulants.

The study was funded by the Military Operational Medicine Research Program.

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